1. Field of the Invention
This invention generally relates a magnetic disk apparatus, a method for adjusting performance of the magnetic disk apparatus, and a method for accessing a magnetic disk, and more particularly to a magnetic disk apparatus performance adjusting method that is executed by magnetic disk apparatuses, which can change the number of sectors included in each cell set on a magnetic disk, to realize uniformalization of data access times of the magnetic disk apparatuses, a magnetic disk apparatus that executes the method for adjusting magnetic disk apparatus performance, a method for accessing a magnetic disk that is executed on a magnetic disk apparatus whose performance is adjusted by method for adjusting the magnetic disk apparatus performance, and a magnetic disk apparatus that executes the method for accessing a magnetic disk.
2. Description of the Related Art
Data access by a magnetic disk apparatus is executed with an address using a Logical Block Addressing (LBA) format that is a system for attaching logical numbers to all sectors (a sector is a unit of data recording and reproduction). A method for allocating LBA differs depending on a magnetic disk apparatus. Usually, the method for allocating LBA realizing high access efficiency is adopted.
When a storage capacity of the magnetic disk apparatus used for data access in such a form increases, it is inevitable that yield of manufacturing thereof falls.
Under such circumstances, a recent magnetic disk apparatus adopts a method of securing a storage capacity as the whole device (a storage capacity guaranteed as a standard of a product) by setting an optimum track per inch (TPI) and an optimum bit per inch (BPI) for each head.
In other words, the TPI and the BPI are reduced for low-performance heads and, in order to secure a storage capacity decreased by the reduction in the TPI and the BPI, the TPI and the BPI for high-performance heads are increased to secure a storage capacity as the device as a whole.
A method of not using defective heads and defective cylinders to obtain a magnetic disk apparatus with a small storage capacity is also used.
It is assumed that there is a magnetic disk apparatus which should be originally manufactured with a storage capacity of 100 gigabytes, but has a defect in a part of heads. The magnetic disk apparatus cannot realize the storage capacity of 100 gigabytes due to the defect. However, in a case that the storage capacity of 50 gigabytes can be realized, the magnetic disk apparatus is manufactured as a magnetic disk apparatus with a storage capacity of 50 gigabytes.
As a technique related to the invention, Japanese Patent Laid-Open No. 8-255412 discloses an invention concerning an adaptive zone recording method. According to the method, recording zone boundaries are set individually on the basis of actual measurements of performance of respective transducers (transducers for readout and writing), instead of setting recording zone boundaries simultaneously for all recording surfaces in advance on the basis of estimated characteristic values of heads.
When the method of making storage capacities identical in all magnetic disk apparatuses by adjusting TPIs and BPIs is used, it is possible to manufacture magnetic disk apparatuses having an identical storage capacity. However, since a position of LBA differs because of differences of the TPIs and the BPIs, seek times of heads are different. As a result, random access performances are not identical.
For example, whereas it is possible to perform data access with a seek amount of a certain value in a certain magnetic disk apparatus, a seek amount larger than that value is required in another magnetic disk apparatus. Thus, random access performances are not identical.
When the method of obtaining a magnetic disk apparatus with a small storage capacity by not using defective heads and the like is used, a hardware structure of heads of the magnetic disk apparatus is different from that of a magnetic disk apparatus that is originally manufactured with a small storage capacity. Thus, seek times of heads are different and random access performances are not identical.
For example, in an apparatus that is originally manufactured as a magnetic disk apparatus with a storage capacity of 50 gigabytes, it is possible to perform data access with a seek time of a certain value. On the other hand, in an apparatus that is manufactured as a magnetic disk apparatus with a storage capacity of 50 gigabytes by not using defective heads included in a magnetic disk apparatus with a storage capacity of 100 gigabytes, since weight of heads increases, a seek time larger than that value is required. As a result, random access performances are not identical.